Dual duct air conditioning system



p 1952 c. M. ASHLEY ETAL 2,609,743

. DUAL DUCT AIR CONDITIONINGSYSTEM Filed Jan. 16,1947

JNVENTOR. f1 4M; 7

iatenteci Sept. 9, 1952 DUALDUCT AIR CONDITIONING SYSTEM Carlyle M. Ashley, Fayetteville, and William L. McGrath, Syracuse, N. Y., assignors to Carrier Corporation, Newark, N. J., a corporation of Delaware Application January 16, 1947, Serial No. 722,322

14 Claims.

This invention relates to air conditioning, and

more particularly-to a method and system of the so-calleddual-duct type for conditioning a building structure containing a plurality of enclosed areas.

The chief object of the presentinvention is to provide a method of operation of an air conditioning system inwhich ventilation and humidity requirements, room air movement, and transmission gains or losses are compensated for or maintained by the supply of a substantially constant volume of primary air in each areaand in which internal heat loads arising from occupants, lights, sun load, and the like, are compensated for by the supply of a variablevolume of secondary air at a substantially constant predetermined temperature. l

An object of the present invention is to provide an air conditioning system in which primary air for supply to the areas being conditioned may be treated to compensate for transmission gains or losses and supplied to a plurality of areas bein conditioned while return air from the areasbeing conditioned may be cooled to .pre-determined temperature and again supplied to each area in a volume varied to compensate for internal heat factors present therein.

A further object is to provide an air conditioning system including control means which maybe adjusted to permit return air to be used as a source of supply of primary air and in which outside air may be utilized as secondary air with I or without some proportion of return air from the; areas being conditioned.

A still further object is to provide an air conditioning system including separate supply members for primary and secondary air, so arranged that, under; peak load conditions, both primary air and secondary air supplied to the areas being conditioned are at a minimum temperature. The heat load present under peak load conditions is absorbed by the combinedstreams of primary and secondary airthereby eliminating the necessity for large ducts which would be required if one stream of air were heated and the other were cooled under peak load conditions.

Thisinvention relates to a method of air conditioning abuilding structure containing a plurality of enclosed areas in which the steps consist in supplying a constant volume of primary air to each area being conditioned to compensate for transmission gains or losses, the temperature and humiditylof the primary air being adjusted in accordance with conditions of temperature existing exteriorly of the structure and the humidity being'adjusted to maintain a desired degree of humidity in the areasbeing conditioned, supplyinga volume of secondary air at a predetermined temperature to the areas being conditioned, and varying the volume of secondary airsupplied to each area inaccordance with the internal and solar heat factors present therein.

This invention further relates to an air conditioning system which comprises in combination means for treating primary air to desired conditions of temperature and humidity, means for supplying a substantially constant volume of primary air at the desired temperature to each of a plurality of areas to be conditioned to compensate for transmission gains or losses, means for conditioning secondary air to a predetermined temperature, means for supplying such secondary air at the predetermined temperature to a plurality of areas being conditioned, and means for varying the volume or secondary air supplied to each area in accordance with internal and solar heat factors present in the area. 1

. The attached drawing illustrates diagrammatically an air conditioning system adapted for use in practicing the method of the present invention.

Referring to the drawing, there is shown an air conditioning system which includes! a central station 2 to condition primary air. The equipment provided at central station 2 includes a casing 2, dampers 3' to adjust the volume of outside air drawn into station 2, a filter t, a preheating coil 5,'a dehumidifying coil 6,a reheating coil I, and a fan 8. The central station system so described is well-known in the industry. Fan Sdraws air through dampers 3 and through the various elements of the station, supplying the treated air through duct 9 and run-outs 10 to distributing units ll, disposed in areas l2 to'be conditioned. Units H are more fully described hereafter.

A second central station I3 is provided to treat Q secondary air for supply to the areas being conditioned. Station l3 includes a casing [3' a cooling coil [4 and a fan [5, which serves to supply cooled secondary airthrough duct 16 and. run-out ii to units l l. The dry bulb temperature of the secondary air supplied to the areas beingconditioned does not exceed Air is' withdrawn from the areas being conditioned through grilles l8 and duct I9, being drawn within the second central station [3 by fan [5. l

Cooling coil l4 may be operated by separate refrigeration equipment or, if desired, it may be operated by the same equipment designed tOOIJ- erate dehumidifying'coil 6 of station 2. Suitable controls 3?,- 38, and 39 as indicated diagrammatie cally are provided to a sure that the temperature and humidity of primary air are adjusted in accordance with conditions exterior of the'building to maintain design conditions. A suitable control 40 is provided to regulate the temperature of the secondary air in accordance with design conditions.

A duct 20 connects central stations 2 and;l3. A second duct 2| connects central station 2 and duct [9; dampers 23 are disposed in central station 2 between preheating coil 5 and dehumidifying coil 6. Duct 20 is connected to central staftion 2 at a point between dampers 23 and coil Damper 24 is'provided in duct 20.

V I Closing. of dampers 23 and opening of damper 24 permits outside air to be supplied through duct 20 to the second centralv station I3.

A damper 25 is placed in duct is at a point between the second central station and the juncture of duct 2| with duct 19. A damper 26 is placed in duct 2 I; closing of damper 25 and opening of damper 26'permits return air fromthe areas being conditioned to bypass the second central station [3 and to be supplied to central station 2. It will be understood the position of such operation is within the purview ormy invention. The treated primary ainis then supplied in a substantially constant volume sufficient for ventilation purposes of each area through ducts 9 and run-outs Hi to the various units ll disposed in areas 12 being conditioned. The primary air is discharged from units l l at high velocity, thereby inducing streams of air from the area and secdampers may be varied as desired to permit suitable proportions of outside air and return air to be supplied to either central station 2 or central station l3.

.H may consist of a c sing 21 separated into chambers. 28 and 29. Primary air. discharged through run-out l0 enters chamber 28, while sec: ondary air discharged through run-out I! enters chamber. 29. A .grille 3B is placed in unit H to permit the streams of primary and secondary airto. be dischargedinto the area being conditioned. A damper 31 is placed in chamber 29.to vary the volume of secondary air. supplied to the area. Damper 3| may be actuated by any suitable means 3.2. Such means may be manually or. auto: matically operable to vary the volume of second.-. ary air supplied to the area in accordance with or in'response to the internal heat factors present therein.

If desired as indicated in the drawing, the 1311-5.

mary. and secondary air supplies may be separated, primary air being discharged in unit H while secondary air is discharged into any or all of the. areas being conditioned at an outlet 35 remote from the place of discharge of primary air. Of course, in such case, suitable members 38. are provided to permit the volume of secondary air to'be varied as described above. Preferably, in the present invention, primary air is supplied to the units at a static pressure of. within the range of about .2" to about .5" and at a velocity of about 1500 feet to about three thousand feet per minute. Secondary. air may be supplied at a velocity barely suificient toassure that it enters the area being conditioned. The discharge. of primary air at high velocity into the room. being conditioned induces a flow ofsecondary air. and room air into the primary air stream. The. induced air. will be made up of secondary air and air drawn from the room, the respective proportions thereof depending upon the volume of secondary air supplied to the area. The total amount of primary air and induced air remains substantially constant, thereby maintaining a pre-deterrnined constant air movement within each area being conditioned.

Assume the system as described is in operation undersummer conditions. Primary air is drawn 11;

into station 2 by means of fan 8 and is treated to attain desired conditions of temperature to offset transmission gains or losses in the areas being conditioned. In other words, the temperature of theprimary air is adjusted in accordance with conditions of temperature existing exteriorly of the structure, while the humidity of the air is adjusted if necessary-- to maintain the desired humidity in the areas being conditioned. If desired, the primary air may be treated in addition to compensate for some'fixed portion of the internal heat load; it will be understood the expression to compensate for heat gains or losses as used herein contemplates that some minor por-. tion of the internal heat load may be taken care of if desired by the primary air supply in addition to strict transmission gains or losses and such ondary air to mix with the primary air stream to maintain a substantially constant air movement within the area being conditioned.

Return air is withdrawn from the areas being conditioned through duct I9, passed through cooling coil M or central stationv l3 to adjust its temperature to a predetermined point, say 55F" and is again supplied to the areas being condi: tioned throu h duct l6 and run-outs II. The volume of secondary air supplied to each area is, adjusted in accordance with the internal heat load and direct solar load present in each area by means of damper- 3| which may-be actuated man,-.v ually or automatically in response to the tern-r. perature of the area being conditioned as indie. cated by control 32.

Under peak load conditions, both primary air andsecondar-y air supplied to the. areas is cooled, permitting both primary and secondary ducts to be, used to offset the maximum heat loads im-. posed upon the. system. Such procedure permits. a reduction in duct capacity required for peak loads, thereby reducing the initial cost of the system. The cooled secondaryair, supplied at a substantially constant temperature to the areas being conditioned, may be .throttled freely, it re-. quired, without affecting the ventilation, humid-. ity control, or airmovement within the areasbe-- ing conditioned.

Under conditions of winter operation, secondary air, preferably, is still supplied as cold air at a substantially constant predetermined temperature to compensate for internal heat factors present in the areas being conditioned.

If desired, under winter conditions, to decrease the. cost of operation of the system, dampers 23 to 26 inclusive may be adjusted to permit outside air, in a volume at least sufiicient for ventilation requirements in the areas being conditioned, to be supplied to central station l3, cooled, if required, and supplied to the areas being conditioned as secondary air. Return air may be directed through duct 2i to central station: 2; the return air may be heated, as required, at central station 2 and supplied in a substantially constant volume as primary air to the. areas being; conditioned. Under the conditions described, any suitable proportions ofreturn and outside air maybe supplied as primary or secondary air to the areas being conditioned. It is essential, however, that a sufficient volume of outside air be supplied to'the areas for ventilation purposes.

It will be understood that under all conditions, the stream of primary air, whether composed of W5 i? l FF. return 3 a m xt h reqt is t a ed c sa r. h midit e ire me t 15 ra s s i a n 1' 05. 93 5%??? rea nd; s s pli in as bs ntia y Q ...ni q ume a ar a. T ecpeda y air is es a. pr er in d. t m eratur i' if r quired, and is supplied to each area in a volume -Ed t 9 1 9 ite a' nd .3 1 solar heat loads present in each. separate area We have described a system in which primary air is, supplied t a high velocity. It w ll. be understood primary air may be supplied at a relai ly w v l e a 9 mass. per. mi

ute, if desired. Under such conditions, the secondary air is supplied at a greater velocity than the velocity described in order that the combined velocities of discharged primary and secondary air induce and maintain a desired air movement within each area being conditioned. Under such circumstances, velocityof the secondary air may vary inversely as the volume of the secondary air thereby maintaining substan-' tially constant air movement in each area being conditioned.

The present invention provides a simple and inexpensive air conditioning system in which sufficient outside air is provided to compensate for the ventilation requirements of each area being conditioned. Such airmay be treated tocompensate for conditions of humidity and trans-.

mission gains or losses in each separate area;

preferably, such air is supplied in a substantially constant volume and at a velocity suificienty great tomaintain substantially constant movement of. air within each area being conditioned. The costs of operation of this systemare greatly decreased since alarge volume of return air may be utilized under summer. operating conditions while under winter operating conditions a large volume of outside air maybe utilized to decrease the refrigeration required. 9

The secondary air is cooled to a substantially constant temperature to compensateifor internal heat factors and sun load present in each separate area. The system is highly flexible permitting full advantage to be taken of changes in temperature and humidity exteriorly of i the structure to decrease the quantity oirefrigeration required thereby decreasing operating costs.

Under conditions of peak load during summer operation, for example, both sources of supply may provide cold air forus'e in the areas being conditioned, thus eliminating to a large extent the expense involved in the provision of separate ducts, each large enough to compensate for To de demand under peak load conditions. crease the cost of operation of the system, depending upon the conditions of operation, outside air may be employed as a source of secondary air while return air may be employed as a source of primary air.

A modification of the present invention is described in copending application of Carlyle M. Ashley, Serial No. 722,321, filed January 16, 194.7. i

While we have described and illustrated a preferred embodiment of our invention, itwill be understood our invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

'- We claimf "1. In the method of air conditioning a building structure containing a plurality of enclosed areas, the steps which consist in under summer operating conditions cooling fresh air to a desired temperature to form a source of primary air, supplyinga substantially constant volume of the primary air from said source to each area to be conditioned to compensatefor transmission gains and ventilation requirements in that area, providing a supply of cooled, secondary air at a central station, connecting the supply of cooled secondary air to the areas to be conditioned to supply a volume of cooled secondary air to said areas, and varying the volume of cooled secondary air supplied in each area in accordance with the internal and solarheat factorspresent therein.

-.2.'1In the method of air conditioning abuilding structure containing a plurality of enclosed:

areas, the steps which consist in under summer operating conditions treating fresh air to adjust the temperature thereof inaccordance with conditions existing exteriorly of the structure and the humidity to maintain adesired degree of humidityin the areas being conditioned, supplying 'asub'stantially constant volume of the treat,- edfresh air to each area being conditioned to compensate for transmission gains and ventilation requirements in that area, providing a'supply of cooled secondary air at a. central station, connecting the supply of cooled secondary .air to.

3-. In the method of air conditioning a building structure containing a plurality of enclosed areas, the steps which consist under summer op. erating conditions in treating fresh primary air to adjust the temperature thereof in accordance with conditions existing exteriorly of the building structure and the humidity to maintain a desired degree of humidity in the areas being conditioned, supplying a substantially constant volume of treated primary air in each area to be conditioned to provide for ventilation requirements and tocompensate for transmission gains or losses, returning air from the areas being conditioned to a central station, treating the return airat the central station to pro-determined temerature to form a source of secondary air for the areas being conditioned, supplying secondary air to the areas to be conditioned, and varying the volume of secondary air supplied in each area in accordance with the internal and solar heat factors present therein.

4. In th method of air conditioning a building structure containing a plurality of enclosed areas, the steps which consist in withdrawingair from the areas being conditioned, treating such air to a desired temperature at a central station to form a source of'supply of primary air, supplying a substantially constant volume of primary air in each area being conditionedto compensate for transmission gains or losses, supplying outside air as secondary air toeach area to be conditioned in a volume at least suificient to compensate for ventilation requirements of the area, and varying the volum of secondary air supplied in each area in accordance with the internal and solar heat factors present thereim 5. In the method of air conditioning a building structur containing a plurality of enclosed areas, the steps which consist in treating a priji mar-y mixture of outside and return air to de-I and varying the volume of secondary air supplied in each area in accordance with the internal and solar heat factors present therein.

6. A method of air conditioning according to claim which the dry bulb temperature of the 7 secondary air; supplied the areas: being conditioneddoescnotexceed 65F.

"LA method. according; to claim 1 inv which. the duct. velocity of the primary air supplied. to each area being conditioned is at least 1500 F... P. M.,. discharge: of primary air into: each area being conditioned. inducing a substantially constant total. volume. of. secondary air and room air intothe: primary air: stream to attain. a predetermined. air morement within eacharea.

1 8.- Amethod; according. to claim 2 in which the duct, velocity of: the; fresh .air discharged. in each area. being: conditioned is at. least. 1500 F. P. M., the stream. of. freshair discharged into each area being conditioned inducing streams of secondary air and room. airin a substantially constant total volumathcreby-maintaining a predetermined air movement withinieach area,

. 91'..ID., an air conditioning system, the combination of means for cooling fresh air to a. de-- sired temperature: to; formv a source of primary air; means. for supplying a substantially constant volume of cooled. primary air from said source to. eachiof. a plurality of areas to be conditioned to. compensateior transmission gains and ventilation requirements: in :each area, a central Sta-- tion. for providing a supply of cooled secondary air, means. for connecting the supply of cooled secondary tozsaid' areas: to supply a volume of cooled secondaryair to each area. to be conditioned, and: means for varying the volume of secondary air supplied in each area in accordanca withinternal. and solar heat factors present inthearea.

1.0...111 an air conditioning. system, the com bination of. meansfor treating primary air to desired ccnditions. of. temperature and humidity, means. for supplying a substantially constant volume of primary air to each of a plurality of areas to. be conditioned to compensate. for transmission gains or losses a central. station for con-- ditioning return air to a desired temperature, means for withdrawing air from the. areas being conditioned and for returning such air to the central station, means for supplying the conditioned, return air to each area to be conditioned,

andmeans for; varying the volume of conditioned return. air supplied in each area in accordance with the. internal and solar heat factors present. inthe area.

. 1.1'. In an airconditioning, system, the combination. of a central station for conditioning primary air to. desired conditions oftemperature and humidity, a duct for supplying a substantially constant volume of'treated primary airto each of a plurality ofareas tobe conditioned. to compensate'for transmission gains or losses, units. dis posed in said areasad'apted to receive primary air, means to discharge primary air from each unit into the area to induce flow of air within the area thereby maintaining a substantially constant air movement within the area being conditioned", a. second central station for treating return air from the areas being conditioned to a desired temperature, a duct through which return air is 'withdrawn from at least some of said areas and returned' to the second central station, a duct for supplying conditioned return air to said units, and means ineach unit for regulating the volume ofreturn air discharged in accordance with internal and solar'heat factors present in the area.

'12. In an airconditioning system, the combination of a central-station for conditioning primary 'ai'r to desired conditions of'temperature and humidity, a duct for supplying a substantially constant volume. of treated primary air; to each. of. a. plurality of areas to: be conditioned to com.- pensatefor transmission gains or losses, units. disposed. in saidiareasadapted to receive primary air, means'to. discharge primary air from each. unit, into; the area to induce flow of air within the area thereby maintaining a substantially con.- stantair; movement withinsthe area being conditionecta second central. station for. treating, return air from the areas being conditioned to a desired temperature, a second duct through;

which: returnair is withdrawn from at least some of: said areas andreturned. to the second central station, a third duct: for supplying conditioned.

return air to said units, means in. each unit for regulating the. volume of return air discharged in accordance with internal and solar heat factors. present in the area, a fourth duct connecting the. first central station and the second central station, dampers. to discontinue the flow of outside air through the firstcentral station and. to direct such outside air to the second. central station, a. fifith. duct connecting. the second duct and the first: central. station, and dampers disposed in the fifth. duct and. the second duct to discontinue supply of. return air to the. second central stationwhereby return airmay be. supplied to the areas being conditionedas. primary air and out-- side air may be: supplied as secondary air. in a varied volume in accordance with the internal, and. sola-r'load factors present in the. area.

13. .In themethod. of air conditioning a building structure containing a plurality of enclosed areas,v the steps; which. consist under summer operating conditionsin supplying a substantially constant volume of; fresh, primary air: to each area. of the structure to provide for ventilation requirements, returning air from the areas being conditioned. to a central station, treating the return air: to pro-determined. temperature, supplyi-ng; the treatedireturn air to the areas to be conditioned, and; varying the volume of treated return air supplied in. each area to compensate. for theinternal and solar heat factors present therem.

14. In the method of. air conditioninga building structure containing a plurality of enclosed. areas, the steps which consist, in supplying a con-' stant. volume of: fresh primary air to each area being conditioned to provide for. ventilation requirements and to compensate for transmission gains or losses, returning air from the areas being conditioned to a central station, cooling the return air to predetermined. temperature, supplying the+coeledair to the areas being conditioned, and varying each area the volume of cooled air supplied thereto to compensate for the internal and solar heat factors present therein withoutsubstantial interference with the volume ofcooled air-supplied to the remaining areas.

CARLYLE Mr ASHLEY. WILLIAM L. MCGRATHL REFERENCES CITED The following references are of record in the file of this patent:

UNI'I-ED STATES PATENTS Number Name Datev l d-79 ,406 Davis Apr. 18, 1916 1 ,943 613 Lewis Jan. 16,1934 2,131,725 Chester Oct. 4, 1938 2,168,614- Beeler Aug. 8,1939. 2,345,536 Keep Mar. 28, 1944 2,363,294 Carrier Nov, 21119443- 

